1. Field of the Invention
The present invention relates to an apparatus for measuring a partial discharge, and particularly to an apparatus for detecting a partial discharge when a high voltage rotating electric machine is out of operation or is in operation.
2. Description of the Related Art
In recent years, the size and number of a rotating electric machines are increasing with the increasing scale of plants in general industry, and thus, due to high reliability required for such an electric apparatus, it is necessary to perform maintenance and inspection in a reliable manner so as to prevent an abrupt accident, such as breakdown, from occurring.
Besides, with the greater part of many apparatuses manufactured in the high level economic growth period, 25 years or more have elapsed since their manufacture, and particularly in these electric apparatuses which have worked for a long period, a request for continuous monitoring during the operation becomes very high for the purpose of preventing an abrupt accident from occurring.
Moreover, the Electric Utility Industry Law in Japan or similar laws in other countries was revised on 1996 or will be revised in the future, so that regulations were or will be relieved so that an attempt at voluntary maintenance is strengthened, and an attempt to extend an interval between periodic inspections to a length of about 1.5 times the conventional interval has been carried out, so as to improve management efficiency. From such a point of view, it recently becomes more important to monitor an insulation state during the operation than in the past, and as a monitoring item, importance comes to be attached to a continuous monitoring technique of a partial discharge indicating insulation properties. In a rotating electric machine, when deterioration such as a crack or peeling occurs in an insulating layer of a stator winding by operational stress, a partial discharge is generated at the deteriorated portion by voltage during operation. The deteriorated state of insulation is comprehended by measuring the partial discharge. In general, since the partial discharge of the rotating electric machine or the like is buried in noise, it is necessary to distinguish the partial discharge from the noise so as to measure only the partial discharge. The noise during the operation is the greatest factor among others to make the measurement of the partial discharge difficult.
Many methods have been used for distinguishing a partial discharge from noise and measuring only the discharge of a deteriorated portion when insulation deterioration occurs.
For example, Japanese Patent laid-Open No. Hei. 3-12574 discloses that a partial discharge at the time of starting a rotating electric machine and a partial discharge at the time of a regular operation are respectively measured, and a difference between them is compared. Besides, there is disclosed an abnormality detecting method in which a command is issued so that a partial discharge during a starting period of a rotating electric machine is input to an appropriate device, which then measures the partial discharge quantity during this period and saves the result of this measurement. Then, the partial discharge at the time of the regular operation is measured, so that the saved partial discharge quantity at the time of starting and the partial discharge quantity at the time of the regular operation are compared with each other to find a difference therebetween.
Moreover, for example, Japanese Patent Laid-Open No. Hei. 1-116463 discloses a partial discharge measuring apparatus for a rotating electric machine, which is provided at a predetermined position of a lead for driving the rotating electric machine or outputting power generated thereby, so that a voltage wave and a current wave in a propagation wave of a partial discharge and noise propagating through the lead are detected to determine their polarities, whereby the travelling direction of the propagation wave in the lead is determined from a combination of the thus determined polarities of the voltage wave and current wave, and the partial discharge and the noise are discriminated from each other to detect only the partial discharge.
Besides, computer-aided methods are conventionally used as an insulation diagnosis method for detecting abnormality of insulation. Japanese Patent Laid-Open No. Hei. 3-238370 discloses such a partial discharge diagnosis method in which in the partial discharge measurement of gas insulation equipment, a neural network is made to previously learn a number of partial discharge waveform patterns and their generation factors, so that a partial discharge waveform detected from the gas insulation equipment is classified into a pattern, and a feature of the extracted partial discharge waveform is inputted to the neural network for analyzing a generation factor of the partial discharge.
Moreover, Japanese Patent Laid-Open No. Hei. 1-191071 discloses a monitoring method for a rotating electric machine, in which a high frequency electric quantity based on a discharge extracted from an electric power supply line of the rotating electric machine is attenuated, before measurement thereof, to a level suitable for detection by a detector through an attenuator in which the relation between an operation amount at the time of performing an attenuation operation of a high frequency electric quantity corresponding to a definite discharge quantity and an attenuated output is confirmed in advance, and then, actual measurement is made.
Besides, in the Electric Society Technical Report Second Part No. 402, there are reported insulation diagnosis methods for other various power plants in operation, or partial discharge measurement methods and apparatuses.
As a typical example of such conventional techniques, FIG. 7 shows an example of insulation abnormality detection for a rotating electric machine, and the structure and operation of this conventional technique will be described with reference to FIG. 7.
FIG. 7 is a structural view explaining an abnormality detecting method for a rotating electric machine disclosed in Japanese Patent Laid-Open No. Hei. 3-12574. In FIG. 7, reference numeral 1 designates a three-phase electric motor, and three-phase lines 3 are connected to windings U, V, and W of the respective phases of a stator 2. Solid capacitors 4 having little loss at high frequencies are connected as coupling capacitors to the lines 3. A detector 5, a changeover switch 6, a noise filter 7, and a partial discharge measuring portion 8 are connected to the solid capacitors 4. The partial discharge measuring portion 8 is constituted by a partial discharge measurement portion 9 for measuring a partial discharge at the time of starting the electric motor 1 and a partial discharge in a regular operation thereof, a discharge input time control portion 10 for controlling a partial discharge input time, and a discharge data storage portion 11 for storing discharge data.
A method of determining a deteriorated state by the thus structured conventional abnormality detecting method will be described. In the foregoing structure, it is assumed that there is a relation, as shown in FIG. 8, between the time from the start of the electric motor 1 to the regular operation and load current. From this relation, first, at the time of the start designated by reference numeral 11, a partial discharge is measured by the partial discharge measuring portion 8 through the solid capacitors 4. In this case, from FIG. 8, the start time 11 is as short as 12 seconds (even in a large machine, the time is 30 seconds), inputting of the partial discharge in the start period is instructed by the discharge input time control portion 10, the partial discharge in this period is measured, and a measurement result is stored in the discharge data storage portion 11, so that a partial discharge quantity at the start time is secured.
Next, the motor proceeds to a regular operation designated by reference numeral 12. In this case, the output in the regular operation is changed according to the purpose of use, and reference numeral 121 designates an operation of 30% output; 122, an operation of 60% output; and 123, an operation of 100% output. The partial discharge is measured by the partial discharge measuring portion 8 through the solid capacitors 4 in the state of the operation 123 of 100% output. Then, the difference between the partial discharge quantity at the start time stored in the discharge data storage portion 11 and the partial discharge quantity at the time of the regular operation is compared, and from this result, deterioration in the windings of the stator 2 of the electric motor 1 is judged. The judgement of the winding deterioration is based on the measurement result shown in FIGS. 8 and 9. FIG. 8 shows the relation between the time and load current, and FIG. 9 shows the maximum discharge electric charge quantity at the start time and the regular operation time. When insulation deterioration or fixing force deterioration occurs in the winding of the electric motor 1, as shown by a characteristic 131 of FIG. 9, the difference in the maximum discharge electric charge quantity between the start time and the regular operation time remarkably appears. In the case where the insulation deterioration or fixing force deterioration does not occur in the winding, as shown by characteristics 132 and 133 of FIG. 9, there is little difference in the maximum discharge electric charge quantity between the start time and the regular operation time. In this way, winding abnormality is judged.
In a partial discharge measuring method and measuring apparatus during operation, the most serious problem is to distinguish a partial discharge from noise and to reject it. Besides, in view of improvements in economical efficiency, reduction of costs in maintenance of a rotating electric machine is greatly demanded. With respect to a high voltage electric motor in a power plant or the like, which is an object to be measured in the present invention, a large number of electric motors are operated at the same time. Thus, noise due to operation other than the motor to be measured (hereinafter referred to as a measurement objective motor) is very remarkable, and partial discharges generated in the motors other than the measurement objective motor are also noise. As described above, a problem to be solved is to effectively measure a partial discharge in a large number of rotating electric machines at low cost and after rejecting noise under a noise rejection condition according to respective rotating electric machines, and to perform abnormality monitoring of the rotating electric machine.
In the foregoing conventional abnormality detecting method of the rotating electric machine, as disclosed in Japanese Patent Laid-Open No. Hei. 3-12574, the partial discharge at the time of start of the rotating electric machine and the partial discharge at the time of regular operation are respectively measured and compared with each other to find a difference therebetween. Besides, inputting of the partial discharge during the start period of the rotating electric machine is instructed, so that the partial discharge quantity during this period is measured and the result of this measurement is stored. Then, the partial discharge at the time of regular operation is measured, and the stored partial discharge quantity at the time of start and the partial discharge quantity at the time of regular operation are compared with each other to find a difference therebetween. However, in this prior art, a specific method of noise rejection techniques is not definitely disclosed.
With respect to noise rejection techniques, there is a method disclosed in Japanese Patent Laid-Open No. Hei. 1-116463. In the structure of a measurement apparatus disclosed herein, signals are judged and are measured, and an obtained signal represents a partial discharge. Thus, in order to reject noises of a number of partial discharge sensor signals of a number of rotating electric machines, the structure of the measurement apparatus becomes large, which is contrary to reduction in costs.
Besides, when the technique disclosed in Japanese Patent Laid-Open No. Hei. 3-12574 is considered in view of reduction in costs, although FIG. 5 of this reference shows a changeover switch 7, there is no description thereof. That is, noise rejection and reduction in costs are not taken into consideration.
Besides, for noise rejection techniques, insulation diagnosis and insulation monitoring of a number of apparatuses, it is indispensable to use a calculator. The foregoing Japanese Patent Laid-Open No. Hei. 3-238370 discloses a partial discharge diagnosis method in which in the partial discharge measurement of a gas insulation apparatus, a neural network is used instead of diagnosis heretofore carried out by an expert having a rich knowledge as to partial discharge, and diagnosis is possible for not only a well-known partial discharge waveform but also an unknown partial discharge waveform, and automating is possible. However, there is no technical concept that noises are rejected from a number of rotating electric machines under respective noise rejection conditions, and data management is made.
The present invention is intended to solve the foregoing problems, and an object of the invention is to provide an abnormality detecting apparatus for a rotating electric machine in which one partial discharge measurement element is used to arbitrarily select signals of a plurality of partial discharge detectors provided respectively to a plurality of rotating electric machines, and noise rejection according to various noise rejection conditions is carried out from the signal by using software, so that partial discharge of the plurality of rotating electric machines can be detected with high accuracy.
According to one aspect of the invention, an abnormality detecting apparatus for a rotating electric machine for measuring a partial discharge generated by abnormality of the rotating electric machine, comprises a plurality of partial discharge detectors for detecting a partial discharge of the rotating electric machine; a switching unit for selecting one arbitrary signal from the plurality of partial discharge detectors; a partial discharge measurement element for measuring a signal of the selected partial discharge detector; a computer for arbitrarily selecting one of the plurality of partial discharge detectors or sequentially selecting the plurality of partial discharge detectors, for carrying out measurement, noise rejection, insulation diagnosis judgement, and data management for the respective partial discharge detectors in accordance with a measurement condition, a judgement condition, and a management condition previously determined for the respective partial discharge detectors, and for displaying a measurement result; and a controller for controlling the switching unit and the partial discharge measurement element from the computer.
According to another aspect of the invention, an abnormality detecting apparatus for a rotating electric machine for measuring a partial discharge generated by abnormality of the rotating electric machine, comprises a plurality of partial discharge detectors for detecting a partial discharge of the rotating electric machine; a switching unit for selecting three arbitrary signals from the plurality of partial discharge detectors; a partial discharge measurement element for measuring the selected three signals of the partial discharge detectors; a computer for arbitrarily selecting three of the plurality of partial discharge detectors or sequentially selecting three of the plurality of partial discharge detectors, for carrying out measurement, noise rejection, insulation diagnosis judgement, and data management for respective partial discharge detectors in accordance with a measurement condition, a judgement condition, and a management condition previously determined for the respective partial discharge detectors, and for displaying a measurement result; and a controller for controlling the switching unit and the partial discharge measurement element from the computer.
In a preferred form of the invention, the plurality of partial discharge detectors comprise a plurality of first partial discharge detectors set inside of a frame of the rotating electric machine.
In another preferred form of the invention, the plurality of partial discharge detectors comprises a plurality of second partial discharge detectors set at high voltage buses of the rotating electric machine.
According to still another aspect of the invention, an abnormality detecting apparatus for a rotating electric machine for measuring a partial discharge generated by abnormality of the rotating electric machine, comprises a plurality of first partial discharge detectors set inside of frames of a plurality of rotating electric machines; a plurality of second partial discharge detectors set at high voltage buses of the plurality of rotating electric machines; a switching unit for selecting one arbitrary signal from the plurality of first partial discharge detectors and one arbitrary signal from the plurality of second partial discharge detectors; a partial discharge measurement element for measuring the selected signals of the first and second partial discharge detectors; a computer for arbitrarily selecting one of the plurality of first partial discharge detectors and one of the plurality of second partial discharge detectors or sequentially selecting the first partial discharge detectors and the second partial discharge detectors, for carrying out measurement, noise rejection, insulation diagnosis judgement, and data management for the first partial discharge detectors and for the second partial discharge detectors in accordance with a measurement condition, a judgement condition, and a management condition previously determined for the first partial discharge detectors and those for the second partial discharge detectors, and for displaying measurement results; and a controller for controlling the switching unit and the partial discharge measurement element from the computer.
Preferably, the partial discharge measurement element comprises a first narrow band detection circuit and a second narrow band detection circuit in which propagation characteristics of a signal is taken into consideration, and the partial discharge is discriminated and measured through a comparison between a first narrow band signal and a second narrow band signal.
Preferably, a detection band of the first narrow band detection circuit and the second narrow band detection circuit is 5 to 50MHz, and the comparison between the first narrow band signal and the second narrow band signal is a signal intensity comparison.
Preferably, the plurality of first partial discharge detectors set inside of the frames of the rotating electric machines are temperature detection elements and lead lines.
Preferably, the plurality of first partial discharge detectors set inside of the frames of the rotating electric machines are antennas, a center frequency of an electromagnetic wave detected by the first narrow band detection circuit and the second narrow band detection circuit constituting the partial discharge measurement element is within a range of 300 MHz to 3 GHz, and the comparison between the first narrow band signal and the second narrow band signal is a signal intensity comparison.
Preferably, the plurality of second partial discharge detectors set at the high voltage buses of the rotating electric machines are coupling capacitors and detection elements.
Moreover, in the apparatus, in accordance with previously programmed contents, each of the partial discharge detectors is arbitrarily selected for measuring a partial discharge in a measurement frequency band set for each of the partial discharge detectors, so that the partial discharge is discriminated by a comparison between the first narrow band signal and the second narrow band signal for each of the partial discharge detectors to reject the noise, whereby insulation diagnosis judgement is made and data management is made for each of partial discharge measurement portions.
Preferably, noise is discriminated and rejected from the partial discharge through a difference in reaching time to the first partial discharge detectors and the second partial discharge detectors, so that insulation diagnosis judgement is made and data management is made for each of partial discharge measurement portions.
Preferably, the output signal intensity of the first partial discharge detectors is compared with the output signal intensity of the second partial discharge detectors so that noise is discriminated and rejected from the partial discharge, and thereafter insulation diagnosis judgement is made and data management is made for each of partial discharge measurement portions.